Due to the heavy use of wireless communications in both civilian and military environments, there is often a shortage of available communication bandwidth. Traditionally, frequency “bands” have been assigned on a regional or global basis according to specific types of usage, such as commercial AM and FM radio, commercial VHF and UHF television, citizens band radio, licensed amateur radio, cellular telephony, satellite communication, ship-to-shore communication, aviation communication, military communication, and such like. Within many of these bands, such as commercial television and radio bands, specific frequencies or “channels” are assigned to individual entities, such as channels assigned to specific radio and television stations. Typically, such assignments provide for exclusive use of the assigned channel over a designated geographic region.
This traditional approach of exclusively reserving specific communication channels for specific entities generally leads to inefficient use of bandwidth, since at any given time, and in any given location, it is unlikely that all of the assigned channels will be in use. For example, a commercial television station may not have any broadcast coverage in certain portions of its assigned geographic region, and/or may broadcast only at certain times, leaving the assigned channel empty and unused at other locations and/or at other times.
One approach to taking advantage of this unused bandwidth is to use “Cognitive Radio” or “CR” technology. A cognitive radio is a radio that is capable of sensing its local bandwidth environment, so as to determine at any given time what frequencies are unused (so-called “white spaces”) or underused (so-called “grey spaces”). Cognitive radios can then opportunistically use these white and/or grey spaces to communicate with each other without requiring a fixed, dedicated frequency assignment. It is fundamental to this approach that the cognitive radios function as secondary users of whatever channels they select. Therefore, they must effectively monitor the channels at all times for primary, or “incumbent” usage, and avoid any interference with the incumbents.
In particular, with reference to FIG. 1, cognitive radios can be used to form a so-called “Wireless Regional Area Network,” or WRAN. In a WRAN, a base station CR 100 communicates with a plurality of subscriber CR's, or “subscribers” 102. In some implementations where the subscribers are not mobile, they are referred to as “Customer Premise Equipment” or “CPE” CR radios. The base station 100 determines which channels are available at any given time and communicates with the subscribers 102 to direct the usage thereof by the WRAN. In the simplest case, the base station 100 monitors and analyzes the bandwidth environment, selects an available channel, and broadcasts information on that channel to the subscriber radios 102. The base station 100 may also consult a database of known incumbents 104 and their assigned channels, regions, and patterns of usage. When a subscriber radio 102 wishes to join the WRAN, it surveys the local bandwidth environment until the base station 100 is located, and then identifies itself to the base station 100 and joins the network. Once the WRAN is established, the base station 100 coordinates switching of the WRAN to other frequencies from time to time, if and as needed. In FIG. 1, the incumbent 104 is illustrated as not presently broadcasting, thereby leaving its assigned channel free for use by the WRAN. Usage of the available WRAN frequencies is coordinated in some implementations by an exchange of messages 106 between the nodes 100, 102, the messages 106 being referred to herein as “coexistence beacons.” The co-existence beacons can include, for example, requests to use a channel and acknowledgements thereof, as are used for example in an RTS/CTS protocol.
With reference to FIG. 2, the network architecture of a WRAN is a so-called “star” configuration, whereby communication within the network is always between the base station 100 and a subscriber 102.
While methods are known for ensuring the privacy and security of conventional wireless networks, CR based networks are potentially exposed to many more vulnerabilities because of all the additional functionality that they include as compared, for example, to networks based on traditional software defined radios (SDR's). This is because each additional functionality is a potential soft spot for an attacker to gain access to the system, or against which to stage a denial of service (DoS) attack. As a result, besides providing typical traditional forms of security, a WRAN must provide enhanced security mechanisms for these cognitive functions, so as to provide protection not only to nodes of the WRAN, which are secondary users of the spectrum, but also to the primary or “incumbent” users.
For example, in cognitive radio systems, confidentiality and privacy mechanisms must protect not only the data, but also subscriber information, spectrum occupancy information (which may be of interest, e.g. to competitors), and the spectrum management information used by the base station 100 to configure the subscribers 102 and to direct the operation of the WRAN. In particular, when WRAN communication is used in military operations, it may be highly important to the safety of friendly combatants that management messages wherein nodes report their identities and their positions are securely protected.
In addition, the nodes of a WRAN must share whatever frequency channels are available. This can be facilitated by transmitting of co-existence beacons between the nodes, for example beacons transmitted by a node that informs other nodes of an intent to transmit over a specified channel. However, this approach can provide opportunities for a malicious entity to attack the WRAN by transmitting false beacons that confuse the legitimate nodes and deny them access to the WRAN frequency channel(s).
Also, the use of co-existence beacons 106 can provide an opportunity for malicious entities to attack the WRAN by transmitting false beacons that would tend to confuse legitimate nodes and deny them access to the WRAN frequency channels.
What is needed, therefore, is a method for ensuring reliability, security and privacy of communications in a wireless cognitive radio network.